Method for rolling nonwoven fabrics



April 21, 1970 J. J. SUCH ET L METHOD FOR ROLLING NONWOVEN IABRICS 3Sheets-Sheet 1 Filed Feb. 5, 1966 April 21, 1970 J. J. SUCH ET 3,507,943

METHOD FOR ROLLING NONWOVEN FABRICS Filed Feb. 5, 1966 3 Sheets-Sheet 2April 21, 1970 J. J. SUCH ET AL 3,507,943

METHOD FOR ROLLING NONWOVEN FABRICS Filed Feb. 3, 1966 3 Sheets-Sheet 5United States Patent 3,507,943 METHOD FOR ROLLING NONWOVEN FABRICS JohnJ. Such, Wrentham, and Arthur R. Olson, Walpole, Mass., assignors to TheKendall Company, Boston, Mass., a corporation of MassachusettsContinuation-impart of application Ser. No. 492,644, Oct. 4, 1965. Thisapplication Feb. 3, 1966, Ser. No. 524,931

Int. Cl. D04h 1/64; B29g /00; 132% 7/14 US. Cl. 264-103 25 ClaimsABSTRACT OF THE DISCLOSURE A method directed to forming unwoven sheetsof deformable textile materials by rolling is described. Theunsynchronized non-meshing pair of rolls are engraved in a pattern oflands and grooves; the desired pattern is reproduced in the materialwithout registry between the roll patterns. Impregnation, heated rolls,aperture formation, lamination, felting and plying are included amongthe embodiments.

This application is a continuation-in-part of our copending applicationSer. No. 492,644, filed on Oct. 4, 1965, now abandoned.

This invention relates to methods of reforming sheets of deformabletextile fibrous material by permanently displacing and rearranging atleast a part of the fibrous substance to provide a set of discrete,spaced-apart rearranged areas, and to certain products produced by suchmethods. Illustrative of deformable textile fibrous sheet materials arefibrous webs, particularly those with a certain percentage ofthermoplastic fibers; fibrous webs containing a plastic bonding materialin either set or unset condition; and woven or knitted fabrics,including fabrics treated or coated with organic polymeric material,such as artificial leather or adhesive tape. Various embodiments of suchtextile materials may be used alone, or in laminated combination withother sheet materials such as polymeric organic films or paper.

It is known to emboss textile fabrics and films by passing them betweena metal roll patterned in raised and depressed areas, and a solid backuproll. Processes are also known where the pattern to be applied to thefabric or film is divided between the two rolls. An extension of thistype of embossing is found in US. Patent 2,464,301, to Francis. Ingeneral, prior art pressure-embossing processes, on non-woven fibroussheets for example, have been carried out in one of three ways. Bothembossing rolls may be engraved with an identical pattern of areas inrelief and areas in intaglio, so that a relief or raised area on oneroll matches and opposes a relief area on the other roll, creating anarea of high pressure. Conversely, a raised area on one roll may bedesigned to register with an intaglio or depressed area on the otherroll. In both such cases, proper and exact synchronization of both rollsis essential to provide proper registry of the pattern, which isdifficult and expensive to maintain. It is common practice in thecommercial embossing art, therefore, to reproduce all of the desiredpattern on just one roll, and to process the sheet material between sucha roll and a plain, non-patterned roll, such a plain roll varying inhardness from rubber to metal depending on the particular pattern to beembossed. This chief disadvantage of such a process is that the pattern,being impressed by one roll, appears prominent and well-defined only onone face of the material.

We have found that novel and useful results may be realized byprocessing deformable material between a pair of rolls which are bothengraved in a pattern of lands and grooves, as explained more fullybelow. Such a roll system we have found to have novel advantages in therearrangement of fibers contained in deformable textile sheet material,including the printing in relief of a displacement patternsimultaneously on both faces of the sheet, spot-bonding of sheetscontaining pressure-sensitive or thermoplastic material, and to beparticularly suitable for spot-aperturing of both woven and nonwovenfabrics.

It is a primary object of this invention therefore to provide a new anduseful process for rearranging the fibers in a deformable textilefibrous sheet material. It is also an object of this invention toprovide novel products made according to said process.

The invention will be more clearly understood by reference to thefollowing specification and drawings, in which FIGURE 1 is a view,partly broken away, of a preferred apparatus suitable for carrying outthe process of this invention.

FIGURE 2 is a stylized representation of the type of pattern produced bythe apparatus of FIGURE 1.

FIGURE 3 is an alternative pair of rolls for carrying out the process ofthe invention, explained in detail below.

FIGURE 4 is a rearrangement by rotation of the rolls of FIGURE 3.

FIGURE 5 is a partly broken-away view of another pair of embossing rollsuseful in the practice of this invention, in which the angular pitch anddirection of both rolls is the same, but the land and groove width onone roll is twice the land and groove width on the other roll, and bothrolls have their lands and grooves arranged in our preferred helicalpattern.

FIGURE 6 represent the stylized pressure-pattern produced by the rollsof FIGURE 3.

FIGURE 7 is a partly broken-away view of another pair of rolls suitablefor use in this invention, with an upper helically-engraved roll and alower roll with circumferential lands and grooves.

FIGURE 8 represents the stylized pressure-pattern produced by the rollsof FIGURE 5.

FIGURE 9 is a partly broken-away view of still another pair of rollsuseful in the practice of this invention.

FIGURE 10 represents the stylized pressure-pattern produced by the rollsof FIGURE 7.

FIGURE 11 is a view of either surface of one product of this invention.

FIGURE 12 is a cross-sectional view of the product of FIGURE 9.

FIGURE 13 is a view of the surface of a spot-bonded nonwoven fabric madeaccording to the process of this invention.

FIGURE 14 is a view of the bottom surface of a piece of fabric-backedadhesive tape apertured by the process of this invention.

FIGURE 15 is a view of an apertured nonwoven fabric, also made accordingto the process of this invention.

By the term stylized in the references to FIGURES 2, 6, 8, and 10, it ismeant that these are idealized tracings of the pressure areas as made bypassing a sheet of paper and carbon paper through the apparatus. Indealing with the aperturing of nonwoven fabrics, for instance, it willbe appreciated that the apertures may be somewhat oval in nature, due toplastic flow and plastic memory inherent in the fibrous sheet.

Basically, this invention resides in the pressure-deformation andrearrangement of deformable textile sheet material as set forth abovethrough a pair of rolls each of which is engraved in a series of landsand grooves, preferably with at least one of the pair of rolls bearing aland-groove pattern in the form of a series of helices forming a patternof continuous lands and grooves. In this manner, there is imposed on thesheet material a repeating pattern of pressure areas wherein the fibersare permanently displaced, such areas varying from condensed areas toactual apertures, of a generally quadrilateral configuration, formed bythe traverse of a land area on one roll over a land area of the otherroll, as the rolls are caused to rotate. The shape and spacing of thepressure areas will vary with the configuration of the rolls, as setforth more fully hereinbelow.

Referring to what may be regarded as a basic design of apparatus,reference is made to FIGURE 1 which comprises a pair of metal rolls and12 each engraved with what we herein term a helical pattern of lands 14and grooves 16. Rolls 10 and 12 are provided with journals 18 and 20,and are also preferably provided with heavy backup rolls 22 and 24, forequalizing the pressure distribution and for minimizing bowing. Thejournals 26 and 28 of the backup rolls, as well as the journals 18 andof the embossing rolls, are preferentially equipped with rollerbearings, not shown. Pressure may conveniently be applied by an aircylinder or similar device 36, transmitted to the journals bypillow-blocks 30 and 32, the latter resting on a solid bedplate 34.Journals and pillow blocks will be contained in a vertical casing, notshown. Also, provision may be made for conventional heating of theembossing rolls 10 and 12, as by the insertion of electrical heatingelements disposed in cores drilled through said rolls, or by oil, by gasfiring, or the like.

When a deformable textile sheet material is passed through the nip 17between rolls 10 and 12 of FIGURE 1, a series of pressure-areas 52 ofFIGURE 2 is formed. In general, the overall character of thefiber-displacement pattern will comprise three components: a highlycompacted area 52 where a land has traversed a land: more lightlycompressed areas 50 and 51 where a land on one roll has traversed agroove on the other roll; and a substantially unaffected area 48 where agroove on one roll has traversed a groove on the other roll. The degreeto which these areas are permanently impressed onto the deformable sheetmaterial processed between such rolls will depend on the thickness ofthe sheet material, its nature, and the pressures and temperatures usedin processing. At moderate pressures of not more than about 100 poundsper inch of nip width, thin fibrous webs usually show a pattern ofunconnected quadrilateral impressions which may be thinned out areas, ormay be actual apertures, usually bordered by a ridge or grommet of filmsubstance. Such considerations pertain to the processing of nonwovenfabrics of the order of up to 0.005 inch in thickness and of generallylight weight, up to 30 grams per square yard, as set forth in Examples 2and 4 below.

On bulkier deformable fibrous sheet material, especially when weighingin excess of 50 grams per square yard and over 0.005 inch in thickness,and employing moderate pressures of not more than about 100 pounds perinch of nip width, the customarily expected pattern is one of heavilydepressed areas lying within a trough of less depressed material, saidtroughs running diagonally across the deformed sheet and being separatedby ridges of relatively undisplaced material, as shown in FIGURES 11 and12 and explained in Example 1, If the fibrous sheet containsthermoplastic fibers or thermoplastic material dispersed therein, and ifthere is a temperature differential between the rolls 10 and 12, thenthere may be a difference in depth and in degree of permanence between aheated land on one roll traversing a groove on the other roll, and acool land on the other roll traversing a groove on the one roll. Thatis, the semi-affected quadrilaterallyshaped areas 50 and 51 may differslightly in nature. Such differences are also noticed in the processingof plastic masses laminated to fibrous sheet material, such as adhesivetapes, where various patterned or apertured pressure-sensitive adhesivetapes can be produced by the process of this invention, with theapertures either isolated and discrete, or connected by channels whichfacilitate the transmission of moisture and moisture vapor from apertureto apertur Especially in the case of adhesive tapes, the patternimpressed onto the product will vary not only with the physicalvariables of the apparatus, such as design, pressure and temperature,but with the properties of both the adhesive mass and of the backing,such as resilience, elastic memory, etc.

Using a fibrous sheet containing a proportion of thermoplastic fibers,with pressures in excess of about pounds per inch of nip width and withfiber sheets weighing from 60 to 100 grams per square yard, the natureand degree of fiber displacement will vary with the nature of the fibersused. At pressures of pounds per inch of nip width, blends of nylon witha minor proportion of polypropylene give a pattern of heavily depressedareas interconnected by troughs of less heavily depressed material, asmentioned above. Other fibers of lower moduls of resilience, such ascotton, viscose rayon, or modified acrylics, blended with polypropylene,will under the same pressures yield a product wherein the heavilydepressed areas are actual apertures. The preparation of such aperturednonwoven felts is set forth in Example 7, below.

Considerable latitude may be exercised in the design of the rearrangingrolls, as shown in FIGURES 1, 3, 5, 7 and 9, provided that both rollsbear a land and groove pattern, so arranged that maximum pressure isexerted only intermittently and in a set pattern ofquadrilaterallyshaped areas.

In FIGURE 1, both upper roll 10 and lower roll 12 bear a pattern oflands and grooves in helical arrangement. In FIGURE 3, the lands 15 onupper and lower rolls 11 and 13 are shown as a spacer set of parallelellipsoids extending equidistant from the axes of the rolls and in aplane which is inclined relative to the roll axes. So long as theregister of the lands remains as shown in FIGURE 3, the desiredintermittent pattern of pressure areas will be obtained. However, ifeither of the rolls 11 or 13 is rotated through the allipsoidal discsforming the lands on that roll will now be inclined in opposition to theother roll, as shown in FIG. 4. In such a case, the lands 23 on bothrolls 19 and 21 will mate continuously as the rolls revolve at uniformspeeds, provided that the rolls are of the same diameter. Instead ofmaximum pressure being developed intermittently at a set of spaced-apartpoints, the continuous mating of lands 23 and grooves 25 will result inmaximum pressure being delivered in a series of curved lines running thelength of the fabric, which is undesirable. Therefore, we prefer toemploy helically-disposed lands and grooves as shown in FIGURES 1, 5, 7and 9, since the slippage of one roll relative to another has little orno effect on the desired intermittent pattern of pressure areas. This isa unique advantge of the helical configuration, which additionally seemsto distribute roll pressure and roll wear better than separated lands inthe form of inclined ellipsoids.

FIGURE 5 represents a partly broken-away pair of rolls with the samehelical pitch of 20 (20 lead), but with the lands 60 on the upper roll62 twice the width of the lands 64 on the lower roll 66. FIGURE 6represents the displacement pattern created by passing a sheet ofdeformable material between the rolls of FIGURE 5, under pressure. Theelongated and skewed compressed areas thus obtained are the solid blackareas 67 of maximum pressure, where a land on one roll has made atransient crossing of a land on the other roll: the lessseverelydisplaced dotted areas 68, where a land has crossed a groove; and theunshaded areas 69, where the material has been substantially unaffectedby a groove crossing a groove.

FIGURE 7 represents a suitable pair of rolls where the upper roll 70 haslands 72 angularly oriented at a 45 pitch to the roll axis, to makecontact with a lower roll 74 in which the lands 76 are circumferential,being oriented perpendicular to the roll axis, and are not connected,instead of being helically oriented. In FIGURE 8, the pressure-patterndiagram of FIGURE 7, the

dark areas 77, dotted areas 78, and unshaded areas 79 again representthe areas of maximum, intermediate, and minimum pressure, respectively.

In FIGURE 9, the top roll 80 has lands 82 running at a 45 pitch in anortheast-southwest direction while the lands 86 of the bottom roll 84are pitched at 26 in a northwest-southeast direction, the lands on thetop roll being three times the width of the lands on the bottom roll.

FIGURE represents the displacement pattern produced by the rolls ofFIGURE 9, wherein the particular angles and land-widths of the rollsgives rise to a set of elongated quadrilateral maximum pressure points87, similar areas of unshaded minimum pressure 88, and areas of stippledintermediate pressure 89 the quadrilateral areas of maximum pressure 87being bounded fully on each of their four sides by the quadrilateralareas 89 of intermediately compacted fibers and being contiguous at eachof their apices with quadrilateral areas 88 of substantially uncompactedfibers. From the description of the rolls of FIGURES 1, 3, 5, 7 and 9and from their displacement patterns of FIGURES 2, 6, 8 and 10, it willbe apparent that the patterns may vary from squares oriented at 45 tonarrow, elongated slits. The pitch angle of the lands on one roll shouldnot be equal and opposite to the pitch angle of the lands on the otherroll in order to avoid the special case where the lands on one roll meshwith the grooves on the other roll, or the possibility that a land onone roll will remain in such prolonged contact with a land on the otherroll that a maximum pressure area of substantially continuous length isevolved. When the helical pitch on one roll is opposed to the helicalpitch on the other, therefore, the pitch of the lands on one roll shouldbe selected in relation to the pitch of the lands on the other roll sothat on the material being treated, the lines formed by one set of landswill intersect with the lines formed by the other set of lands at anacute angle which is at least In general, the surfaces of the lands in apair of the grooved rolls of this invention may be considered to definethe surfaces of a pair of coacting cylinders in which the sum of theradii of such cylinders is at no time greater than the distance betweenthe centers of the cylinder axes.

The process of the invention will be illustrated by the followingexamples. In each example, the apparatus of FIGURE 1 was used, in whichrolls 10 and 12 and pressure rolls 22 and 24 were of steel and were 3 /2inches in diameter. Pattern rolls 10 and 12 were helically grooved inidentical patterns, with lands 14 0.035 inchwide and grooves 16 0.040inch wide. The depth of the grooves was 0.025 inch, and the helicalpitch or lead was 30.

EXAMPLE 1 A felted nonwoven fabric was prepared according to theprocedure set-forth in US. Patent 2,774,128, consisting of a batt ofeight superimposed card webs, the second and seventh card webs beingcomposed of 85% bleached absorbent cotton fibers and 15% of 1% inch 1.5denier polypropylene staple fibers. All other card webs were composed of100% bleached absorbent cotton fibers. After shrinking the layered battto an extent of 60% in refrigerated caustic, according to US. Patent2,774,128, the result was a nonwoven felt weighing 120 grams per squareyard, with all-cotton surfaces and center, but with a layer of blendedcotton and polypropylene immediately underlying each cotton surface. Inthis form, such a product may be used as a lithographic or generalpurpose wiping pad, like its all-cotton counterpart. However, thematerial is smooth-faced, and lacks gripping action: it tends to ball upwhen used wet; and is has a dry crosswise tensile strength of only about0.2 to 0.3 pound per inch-wide strip.

Felts consisting solely of cotton fibers may be processed under pressureto form a patterned or textured surface, but due to the rapid swellingwhich cotton fibers undergo when wet, an impressed pattern disappearsrapidly when such a pad is wet out with water.

The dry felt containing polypropylene fibers thus prepared was thereforeprocessed according to this invention by passing it through therolls ofFIGURE 1, with both rolls heated to 440 F. A pressure corresponding to94 pounds per inch of nip width was employed. The result was alithographic wiping pad of the general configuration shown in FIGURE 11and in cross-section in FIGURE 12, both magnified about 11 times,wherein diagonal ribs of uncompressed cotton fibers 58 are alternatedwith trough-like grooves 56, the general pattern being unified by thehigh pressure areas 61. In FIGURE 11, the machine direction is from leftto right. These areas 61 represent the spots 52 of FIGURE 2, wheremaximum pressure was exerted by the lands of the heated rolls crossingeach other. Due to the combination of heat and maximum pressure in theseareas, the polypropylene fibers are fused together within the interiorof the felt, thus serving to render the alternating ridge-and-troughpattern insensitive to water. That is, when patterns of this sort aredeveloped by pressure alone on pure cotton felts, the pattern is clearand prominent on the dry material, but disappears when the swellingaction of water disrupts the transient cellulose-to-cellulose bonds thusestablished. For many types of lithographic work, and for generalapplication, distribution, and removal of aqueous and other solutions, acertain degree of surface roughness or corrugated pattern is desirable.The practice of this invention on a mixed-fiber felt of the type setforth above results in a wiping pad which consists in dominantproportion of absorbent fibers, is soft, conformable, and lintfree, yetpossesses a functional corrugated surface which maintains its charactereven when wet out with swelling agents. The dry cross strength of theembossed product is about 1.4 pounds per inch-wide strip, or about sixtimes the strength of the unembossed felt.

As an alternative to the above procedure of Example 1, a layer ofthermoplastic fiber may be sandwiched between two layers of all-cottonfelt made in accordance with US. Patent 2,528,793, and the sandwichedpassed through the procedure of Example 1.

Useful products similar in appearance to FIGURE 11 may also be made frombatts of fibers, such as nylon or polyester fibers, which are notnormally regarded as thermoplastic, as illustrated by the followingexample.

EXAMPLE 2 A batt of 3 denier 1 /2 inch nylon staple fibers was processedthrough the apparatus of FIGURE 1 at a pressure of 125 pounds per inchwidth of nip, and with both rolls heated to 420 F. The resulting productwas similar to FIGURE 11, with the quadrilateral areas 61 of maximumpressure converted to unbroken but translucent windows of fused fibersubstance. The presence of over of these fused spots per square inchserves to unify the nylon batt without the use of extraneous bindermaterial, making a nylon felt of this character useful as a batteryseparator in alkaline batteries. Greater strength and decreased porositymay be achieved, if desired, by placing a film of cellophane or otherfilm-forming material in the interior of the nylon batt prior to passingthe assembly between the rolls.

Essentially similar results are obtained when polyester fibers are usedinstead of nylon.

EXAMPLE 3 Using the same pair of rolls as in Example 1, a card webconsisting of 3 denier polypropylene fibers 1% inches long, weighingabout 10 grams per square yard, was processed at a pressure of 94 poundsper inch of nip width, with the top roll heated to about 340 F. and thebottom roll heated to 240 F. The result was the spot-bonded, open,porous nonwoven fabric of FIGURE 13, which is magnified about 35 times.In FIGURE 13, the polypropylene fibers 71 are fused together locally ina set of discrete spaced-apart areas 73, which in the actual fabric,using the roll specifications set forth above, were about inch apart. Ina light, thin web of this nature, the process of this invention ingeneral effects a pattern only in a set of such unified areas where aland on one roll crosses a land on the other roll, the land-groove andgroove-groove combinations being substantially ineffective in alteringthe inter-fiber relationships. The fiber segments lying between thebonded areas 73 are therefore in a soft, flexible and unfused condition,except for the intermittent appearance of fused fiber nodes 75,appearing on one surface of the web.

Such nodes are formed because although the fibers 71 in FIGURE 13 arerepresented as being disposed in a two-dimensional plane, actually thereis a minor but definite third dimension of thickness in any carded webof fibers. Certain fiber segments and fiber ends may be considered asbeing oriented in a path which carries them above and below thetwo-dimensional plane of FIGURE 13. It has been our experience that whenone roll is heated sufficiently to fuse the fibers, with the other rollbelow the fusion point, as in this example, those segments of thethermosensitive fibers which protrude appreciably out of the plane ofthe web toward the more strongly heated roll are fused into small nodesor nodules 75. Not all fibers are thus affected, nor is more than aquite minor part of the length of any one thermosensitive fiberinvolved, but the summation of the effects of such nodes, consideringthat FIGURE 13 represents about one onehundredth of a square inch, is toimpart a distinctly harsh, rasping and dragging hand or feel to the faceof the web which has been processed next to the hotter roll, while theface which was against the cooler roll remains soft and smooth to thetouch.

Such an unexpected effect renders products of this sort especiallyvaluable as coverings for dressings and absorbent articles in general,such as hospital sponges, pads, sanitary napkins and the like. Thenonwoven fabric thus produced has one surface of smooth soft fibersegments lying between spaced-apart discrete areas, extendingsubstantially through the entire thickness of the fabric, where theintercrossing thermosensitive fibers are fused together, while the otherface of the fabric is additionally characterized by a randomly-spacedset of nodes or nodules of fused fiber substance, amounting to over onehundred of such minute points per square inch, which impart a harsh andrasping hand thereto, and a high degree of frictional engagement towardother fabrics or fibrous assemblies. Although esthetically undesirablefor contact with the human body, such a harsh hand frictionally anchorssuch a nonwoven fabric on the surface of layers of cellulose wadding,cotton, wood pulp, or other absorbent fillers which commonly constitutethe major absorbent in pads and napkins. Not only does the frictionalengagement of one face of the nonwoven fabrics of this inventionfacilitate the wrapping operations involved in the preparation ofcombination dressings, but in the final dressing it prevents shifting ordisplacement of the absorbent contents, a common source of complaint incombination dressings employing a cover made from a nonwoven fabricwhich is smooth-surfaced on both faces. To the extent that close contactis maintained between a cover produced according to this invention andthe absorbent filler enlosed by such a cover, transfer of fluid exudateto the absorbent filler is facilitated, lessening the degree ofsaturation of the cover and encouraging a dryer and healthier woundsite.

Although the above specific example was made from polypropylene fibers,it will be obvious that other thermoplastic fibers can be employed, suchas polyethylene, vinyl fibers, plasticized cellulose acetate, and othersynthetic fibers which can be thermally bonded to each other or to otherfibers at temperatures below their decomposition points. I11 addition tothe above example, we have made spot-bonded nonwoven fabrics by theprocess of this invention which contain 25%, 50%, or thermoplasticfibers, the balance being, for example, viscose fibers, or any otherfiber selected for a particular property in the final nonwoven fabric.Fibrous webs containing thermoplastic fibers can, by the process of thisinvention, be laminated to films, to paper, to fabrics, to othernonwoven fabrics, or a multiplicity of such fibrous webs, of varyingcomposition if desired, may be bonded together.

EXAMPLE 4 A further example of the utility of the process of thisinvention is in the preparation of porous pressure-sensitive adhesivetapes, capable of transmitting moisture vapor therethrough and therebydiminishing the skin maceration which frequently accompanies the use ofocclusive, moisture-impervious tapes. The gravity of dermal reactions toimpervious tapes is evidenced by the numerous attempts which have beenmade to render tapes permeable, as by perforating the tape mechanicallywith a series of relatively large holes; or by printing the adhesiveonto a porous backing in the form of disconnected spots as in US. Patent2,940,868; by coating With adhesive a perforated film as in U.S. Patent3,073,303; or by embossing a tape on the adhesive side with a patternedroll which carries a set of raised areas which displace the adhesiveunder pressure, as in US. Patent 3,073,304.

We have found that a novel porous adhesive tape of an unusual andadvantageous configuration in the adhesive mass may be produced bypassing a suitable tape through the rolls of FIGURE 1 as follows:

A pressure-sensitive adhesive tape was made employing an acetate satinfabric base, 225 ends and 78 warp yarns per inch, weighing 3.57 yardsper pound. This fabric was solvent-coated with a heptane solution of acommercial pressure-sensitive adhesive mass comprising pale creperubber, tackifier resins, fillers, and age-resistors.

The tape thus prepared was passed through the nip created by thepatterned rolls 10 and 12 of FIGURE 1, at a pressure of 94 pounds perinch width of nip. The adhesive face of the tape was exposed to the toproll, heated to 425 F., while the cloth face pressed against the bottomroll, heated to 440 F.

The adhesive face of the resulting product is shown in FIGURE 14, themachine direction again being from left to right. Apparently due to thecontinuous traversing and shearing action of the helically-grooved lands14 of the set of rolls, the adhesive mass has been displaced into a setof continuous transverse ridges 81, about 0.010 inch thick, runningdiagonally and uninterruptedly from one selvage edge of the fabric tothe other. In regular alternation with these ridges, and similarlyspaced and oriented, is a set of grooves 83, in which the mass is about0.005 inch thick. Regularly spaced in these grooves or troughs 83 is aset of quadrilaterally-shaped aperture 85, corresponding to a land onone roll crossing a land on the other roll as at 52 of FIGURE 2, inwhich apertures the acetate backing fabric has been crushed and movedaside so that there is no substance therein, under the particularpressures employed.

Porous adhesive tapes prepared in this manner have several advantagesover prior-art tapes. First, they are characterized by a series ofcontinuous diagonal ridges of adhesive mass, the continuity of saidridges providing a greater holding power than prior art patterns inwhich the adhesive is printed in a pattern of isolated spots or areaswhich are completely surrounded by areas containing no adhesive. Second,the actual apertures 86 are interconnected, along any one trough, byareas in which the adhesive is only about one-half as thick as theadhesive on the ridges, thus providing auxiliary paths for moisturevapor from the skin to be transmitted to the air. Such aninterconnection of apertures through a channeled adhesive mass allowsfewer apertures to vent more moisture than is the case where individualapertures are underlaid by an encircling grommet of adhesive mass, andthereby allows the preservation of a higher proportion of the tensilestrength of the backing material.

In cases where the backing of the adhesive is porous, as in the case ofthe acetate fabric above, it is not necessary actually to perforate thebacking. The use of lower pressure and less drastic processingconditions will displace the adhesive mass from thequadrilaterally-shaped areas 85 without cutting through the fabric, butstill allowing moisture-vapor transpiration therethrough due to thechannels 83.

Although the above example was set forth in terms of an acetate fabric,the general procedure is equally applicable to adhesive tapes employinga backing of film, or of a variety of woven or nonwoven fabrics.

EXAMPLE The process of this invention also finds particular utility inthe preparation of novel apertured nonwoven fabrics, as well as in theaperturing of prebonded nonwoven fabrics. Apertured nonwoven fabrics arethose in which a portion of the fibers of an unspun and unwoven web,comprising textile-length fibers, are displaced from their normaloverlapping and intermingled relationship to form a spaced set ofapertures or areas which are essentially devoid of fibers, thus lendingto the nonwoven fabric the appearance of certain woven fabrics. Suchapertured nonwoven fabrics are described in U.S. Patents 3,137,893 and3,150,416, among others, and are of recognized utility as pad coveringmaterials, surgical dressings, disposable towels, and the like.

An unbonded card web of 3 denier inch viscose rayon fibers was saturatedwith an acrylic binder solution of 12% concentration and the wet pickupadjusted to 150%. The wet web Was then passed through the rolls ofFIGURE 1 at a pressure of 94 pounds per inch width of nip, with the bothrolls heated to 430 F. Final drying was accomplished by passing themoist apertured nonwoven fabric over a steam-heated dry can.

The final product is represented by FIGURE 15, magnified about times,wherein the apertured nonwoven fabric 90 consists of a web of rayonfibers 92, marked by a pattern of generally quadrilaterally-shapedapertures 94-, said apertures being essentially devoid of fibersubstance. The apertures occur where a land on the top roll traverses aland on the bottom roll, corresponding to the areas 52 of FIGURE 2. Asmentioned above, in thin and lightweight materials of this character,the land-groove coaction 50 of FIGURE 2 is not apparent, and theapertured nonwoven product is essentially planar and unmarked bytransverse ridges or grooves.

The apertures 94 of FIGURE 15 are characterized by a rim or grommet ofdisplaced fiber segments 96, apparently due to the shearing action ofthe traverse of land over land having aggregated said fiber segments.Such a traverse is initiated at a point, proceeds to its maximum width,and then recedes to a point again as the characteristic quadrilateralshape is generated. Especially when wet, textile fibers are somewhatplastic and are displaced to one side to form the reinforcing fibrousrims 96. This effect is a local displacement confined to the peripheriesof the apertures, and the characteristic card web configuration of thefibers lying between the apertures is essentially undisturbed. Eachreinforcing fibrous rim surrounding an aperture is thereforeindependent, and the rims defining the apertures are interconnected onlyby unrearranged fiber segments.

It is also possible according to this invention to produce comparableapertured nonwoven fabrics from textile webs which have been prebonded:that is, bonded and dried in a separate operation, in distinction to theabove example where bonding and apertures were done simultaneously. Thisis illustrated 'by the following example.

10 EXAMPLE 6 A card web of 1.5 denier inch viscose rayon, weighing 12.grams per square yard, was saturated with 25% of its weight of anacrylic binder and dried, in the conventional manner used for preparingbonded nonwoven fabrics. The bonded material was then wet out withwater, adjusted to about 200% water pickup, and then run through theapparatus of FIGURE 1 at a nip pressure of 125 pounds per inch of nipwidth with both rolls heated to 430 F. The result was an aperturednonwoven fabric resembling the material of Example 4 made from rayonfibers run through the apparatus while wet with binder solution.

In addition to nonwoven fabrics bonded by liquid binders in the form oflatices or emulsions, so-called mixed fiber webs can also be aperturedby the process of this invention: that is, webs which contain a certainproportion of themo'plastic binder fibers such as polypropylene, vinylfibers, or plasticized acetate fibers, mixed with nonbinder fibers. Notonly are the apertured felts thus produced of interesting surfacetexture, with a twill-like structure, but the mechanical integrity andresistance to rupture of the product is of a very high order in view ofthe essentially soft and conformable nature of the material. Thepreparation of such an apertured felt is set forth in the followingexample.

EXAMPLE 7 A blend of bleached absorbent cotton fibers with 25% 1.5denier 1.5 inch polypropylene fibers was carded to give a fibrous battweighing grams per square yard. This fibrous batt was then passedthrough the apparatus of FIGURE 1, with both rolls heated to 450 F. andunder a pressure of pounds per inch of nip. The resulting apertured feltresembled the product of FIGURE 11, wherein the quadrilateral areas 61were actual apertures devoid of fibers, interconnected by diagonaltrough-like depressed areas 56, and with the depressed areas 56separated by soft, uncondensed ribbed diagonal stripes 58, so that atwill effect was prominent.

An especially useful characteristic is the high loft and low bulkdensity of the structure: the measured thickness of 60 thousandths of aninch represents a bulk density, for this weight of web, of 1.1 grams percubic inch or 0.070 gram per cubic centimeter. This open structureenables the fabric to take up relatively large amounts of liquid, ashigh as 11 to 12 times its own weight, as determined in a standard testin which the product is immersed in water for 2 minutes, drained for 2minutes, and weighed.

Another feature of considerable utility and interest is the manner inwhich the tensile properties of the structure are unaffected by thepresence of water or other swelling agent therein. The fabric of thisexample showed a measured machine direction tensile strength of 2.57pounds per inch of Width and about one-fifth of this in the crossdirection. When wet with water these values did not changesignificantly, measuring 2.20 pounds per inch width in the machinedirection and 050* pound crosswidth.

The high absorbency and softness that is characteristic of this materialmakes it especially useful for many hospital product applications suchas sponges, pads, rolls, etc. Its intrinsic softness on both sidesresults from the special feature of this process which locates theapertures, representing the bonding points of the structure, atapproximately the mid-point of the cross section in deep pockets ofbulked fiber.

Carded structures of blended fibers similar to the above have been madein a range of Weights from 40 to 12.0 grams .per square yard and withbinder fiber fractions from 0.10 to 0.50, and non-binder fibers otherthan bleached cotton, including viscose rayon, and Dynel (Union Carbidesmodified acrylic fiber). Especially when synthetic fibers are used, orcoarse deniers of viscose, the resulting apertured felts have acombination softness, conformability and resilience which makes themsuitable for interlining use.

The size and spacing of the aperture made by the process of thisinvention may readily be varied by changing the dimensions, spacing, andorientation of the lands and grooves on the forming rolls. In general,an acceptable range of aperture size seems to be from 0.03 to 0.125 inchin the long diameter of the aperture, at a spacing of from 0.25 and 0.50inch on centers. Customarily, using textile-length fibers of from 1 to 2inches in length, the average fiber length is at least eight times themaximum width of an aperture, though products of a special nature maydemand departure from these dimensional characteristics.

Having thus described our invention, we claim:

1. The method of reforming an unspun and unwoven sheet of nonwovendeformable textile material comprising intermingled fibers of textilelength, characterized by passing said sheet between a pair ofnon-meshing and non-interpenetrating rigid rolls rotating in oppositedirections, said rolls being engraved in a pattern of land and grooves,the sum of the radii of said rolls being at no time greater than thedistance between their axes, the lands and grooves on at least one rollbeing angularly disposed to the central axis of the roll at an angle ofless than 90, a segment only of any land area on one of said rollstransiently traversing a segment of a land area on the other of saidrolls, without synchronization of the lands and grooves of the opposingrolls, whereby maximum pressure is exerted on said deformable textilematerial at a set of discrete and spaced-apart points, intermediatepressure is exerted where a land on one roll has traversed a groove onanother roll, and minimum pressure is exerted where a groove on one rollhas traversed a groove on the other roll, thereby producing a fabrichaving a set of uniformly spaced-apart quadrilateral areas bounded fullyon each of their four sides by an area of lightly-compacted fibers, andeach such quadrilateral area being contiguous at each of its four apicesto an area of substantially uncompacted fibers.

2. The method according to claim 1 in which the pattern of lands andgrooves on at least one of said rolls is helical.

3. The method according to claim 1 in which both rolls bear a helicalpattern of lands and grooves of identical dimensions and of the sameangle and orientation of pitch.

4. The method according to claim 1 in which One roll has a helicalpattern of lands and grooves angularly disposed to the roll axis at lessthan 90, and the other roll a pattern of lands and grooves which areperpendicular to the roll axis.

5. The method according to claim 1 in which the lands and grooves on oneroll differ in width from the lands and grooves on the other roll.

6. The method according to claim 1 in which the lands and grooves on oneroll are helically oriented in a righthand sense, and the lands andgrooves on the other roll are helically oriented in a left-hand sense,the lands on one roll being of greater width than the grooves on theother roll.

7. The method of producing an absorbent wiping pad of improved grippingaction and resistance to collapse when wet which comprises feltingtogether a fibrous mixture comprising absorbent fibers and thermoplasticfibers,

and subjecting the felted mixture to the process of claim 1,

in which process at least one of the rolls is heated sufiiciently toactivate the thermoplastic fibers.

8. The method of producing a spot-bonded nonwoven fabric which comprisessubjecting an unspun and intermingled array of textile-length fiberscomprising thermoplastic fibers to the process of claim 1,

in which at least one of the rolls is heated sufiiciently to activatethe thermoplastic fibers.

9. The method according to claim 8 in which the intermingled array oftextile-length fibers comprises 25% to 100% thermoplastic fibers and to0% absorbent fibers.

10. The method according to claim 8 in which the thermoplastic fibersare polypropylene and the absorbent fibers are viscose rayon.

11. The method of producing a laminated textile article which comprisesforming at least one sheet of unspun and unwoven intermingled fibers oftextile length, comprising thermoplastic fibers, plying at least onesheet of said fibers with at least one substrate layer, passing theassembly between a pair of non-meshing and non-interpenetrating rigidrolls rotating in opposite directions, at least one of said rolls beingheated, said rolls being engraved in a pattern of land and grooves, thesum of the radii of said rolls being at no time greater than thedistance between their axes, the lands and grooves on at least one rollbeing angularly disposed to the central axis of the roll at an angle ofless than a segment only of any land area on one of said rollstransiently traversing a segment of a land area on the other of saidrolls, without synchronization of the lands and grooves of the opposingrolls, whereby maximum pressure is exerted on said assembly at a set ofdiscrete and spaced-apart points, intermediate pressure is exerted wherea land on one roll has traversed a groove on another roll, and minimumpressure is exerted where a groove on one roll has traversed a groove onthe other roll, thereby producing a laminated article having a set ofuniformly spaced-apart quadrilateral areas bounded fully on each oftheir four sides by an area of lightly-compacted fibers, and each suchquadrilateral area being contiguous at each of its four apices to anarea of substantially uncompacted fibers.

12. The method according to claim 11 in which the pattern of lands andgrooves on at least one of said rolls is helical.

13. The method according to claim 11 in which both rolls bear a helicalpattern of lands and grooves of identical dimensions and of the sameangle and orientation of pitch.

14. The method according to claim substrate is a woven fabric.

15. The method according to claim substrate is a film.

16. The method according to claim substrate is a paper.

17. The method according to claim substrate is a bonded nonwoven fabric.

18. The method according to claim substrate is an unbonded fibrousfleece.

19. The method according to claim 11 in which the deformable sheetmaterial is a pressure-sensitive adhesive tape.

20. The method of aperturing an unspun and unwoven sheet of nonwovendeformable textile material comprising intermingled fibers of textilelength which comprises applying to the unwoven sheet a liquid bondingmedium, passing said sheet between a pair of non-meshing andnon-interpenetrating rigid rolls rotating in opposite directions, atleast one of said rolls being engarved in a pattern of land and grooves,the sum of the radii of said rolls being at no time greater than thedistance between their axes, the lands and grooves on at least one rollbeing angularly disposed to the central axis of the roll at an angle ofless than 90, a segment only of any land area on one of said rollstransiently traversing a segment of a land area on the other of saidrolls, without synchronization of the lands and grooves of the opposingrolls, where by maximum pressure is exerted on said deformable 11 inwhich the 11 in which the 11 in which the 11 in which the 11 in whichthe textile material at a set of discrete and spaced-apart points,intermediate pressure is exerted where a land on one roll has traverseda groove on another roll, and minimum pressure is exerted where a grooveon one roll has traversed a groove on the other roll, thereby producinga fabric having a set of uniformly spaced-apart quadrilateral areasbounded fully on each of their four sides by an area oflightly-compacted fibers, and each such quadrilateral area beingcontiguous at each of its four apices to an area of substantiallyuncompacted fibers.

21. The method according to claim 20 in which the pattern of lands andgrooves on at least one of said rolls is helical.

22. The method according to claim 20 in which both rolls bear a helicalpattern of lands and grooves of identical dimensions and of the sameangle and orientation of pitch.

23. The method of producing an apertured nonwoven fabric which comprisesmoistening with water a prebonded nonwoven fabric comprisingtextile-length fibers unified by means of a polymeric binder, passingsaid sheet between a pair of non-meshing and non-interpenetrating rigidrolls rotating in opposite directions, at least one of said rolls beingheated, said rolls being engraved in a pattern of land and grooves, thesum of the radii of said rolls being at no time greater than thedistance between their axes, the lands and grooves on at least one rollbeing angularly disposed to the central axis of the roll at an angle ofless than 90, a segment only of any land area on one of said rollstransiently traversing a segment of a land area on the other of saidrolls, without synchronization of the lands and grooves of the opposingrolls, whereby maximum pressure is exerted on said nonwoven fabric at aset of discrete and spaced-apart points, intermediate pressure isexerted where a land on one roll has traversed a groove on another roll,and minimum pressure is exerted where a groove on one roll has traverseda groove on the other roll, thereby producing a fabric having a set ofuniformly spaced-apart quadrilateral areas bounded fully on each oftheir four sides by an area of lightlycompacted fibers, and each suchquadrilateral area being contiguous at each of its four apices to anareas of substantially uncompacted fibers.

24. The method according to claim 23 in which the pattern of lands andgrooves on at least one of said rolls is helical.

25. The method according to claim 23 in which both rolls bear a helicalpattern of lands and grooves of identical dimensions and of the sameangle and orientation of pitch.

References Cited UNITED STATES PATENTS 1,962,683 6/1934 Dreyfus 2642842,154,940 4/1939 Ives.

2,464,301 3/1949 Francis 264284 XR 2,591,385 4/1952 Sunderhauf 264322 XR2,957,780 10/1960 Stephens 264-284 XR 3,137,893 6/1964 Gelpke 264933,150,416 9/1964 Such 264119 XR 3,351,693 11/1967 Feather 264320 XR3,130,412 4/1964 Fox et a1.

ROBERT F. WHITE, Primary Examiner R. R. KUCIA, Assistant Examiner U.S.C1.X.R.

